fix: type definition for decorator (#529)

* Fix types definition for decorator

* Update import in README

feat: mark library as free of side effects to improve tree sharking

https://webpack.js.org/guides/tree-shaking

Merge branch 'master' into alpha

# Conflicts:
#	package-lock.json
#	package.json

feat(observer): introduce option, allowing to extract even name from …

…event data. Especially useful for 3rd party APIs. Kudos @amiceli for the feature

fix(deps): update vuex to v3.6.2 and fix tests

fix(deps): update dependency @types/socket.io-client to v1.4.36

feat: dedicated entrypoint for the decorator

BREAKING CHANGE: `Socket` decorates is no longer exported out of the root entry point of `vue-socket.io-extended`, use the separate entrypoint instead:

```diff
- import { Socket } from 'vue-socket.io-extended'
+ import Socket from 'vue-socket.io-extended/decorator'
```

chore(tests): fix "[Vue warn]: Component is missing template or rende…

…r function"

feat: Vue 3 support

BREAKING CHANGE: migration to vue 3 (vue 2 is not s

Merge pull request #507

fix(deps): update dependency @types/socket.io-client to v1.4.35